Cathode-ray tube



June 19, 1956 J. PEPER 2,751,515

CATHODE-RAY TUBE Filed Dec. 16, 1952 INVENTOR JAN PEPER AGENT ilnited States Patent CA-THODE-RAY TUBE Jan Peper, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 16, 1952, Serial No. 326,183

Claims priority, application Netherlands January 2, 1952 1 Claim. (Cl. 313-92) This invention relates to cathode ray tubes and to a method of manufacturing same.

Generally, cathode ray tubes comprise a conical or pyramidal-shaped hollow member sealed to a transparent window, the interior of which is coated with a fluorescent screen on which images are recorded by means of a moving electron beam. The fluorescent screen is commonly coated on the side remote from the Window with a metal layer, which is sufiiciently thin to be permeable to electrons, for several reasons. For one thing, it serves to prevent ions produced within the tube from striking the fluorescent screen and detrimentally aifecting its operation. In addition, the metal layer acts as a reflector to light emitted by the screen in a direction away from the window. The latter property requires that the metal layer should be provided with a surface as smooth as possible on the side proximate to an observer viewing the window. Such a smooth surface may be obtained by decanting a solution of film-forming material, e. g., nitrocellulose or borontrioxide, in a suitable solvent, e. g., butyl acetate, on to the inner surface of the fluorescent screen, the irregularities of which have been filled with a vaporizable liquid, e. g., water. The solvent, and thereafter the water, is evaporated off leaving a thin smooth film or intermediate layer upon which metal is deposited, for example, by evaporation to form the metal layer. Since the presence of the intermediate layer in the completed tube is generally detrimental, it is usually evaporated and/or burned out by heating in an oxygen-containing atmosphere, the resultant gaseous products escaping both at the sides of the screen and through minute apertures in the metal layer.

When the film-forming material of the intermediate layer is applied to the fluorescent screen, part of it inevitably finds its way on to the lateral wall of the cathode ray tube, the term lateral wall being understood to mean that part of the tube wall which is adjacent the window or support for the fluorescent screen and which does not act as a window for viewing the image. Consequently, in applying the metal layer to the collecting screen, part of the lateral wall is also covered with metal. In some cases, such metal coating is desirable because when the lateral wall consists of glass or some other non-conducting material, for example, quartz, it is desirable to coat it with a conducting layer to shield the tube-interior from external electrical influences and also to prevent electrostatic charging of the non-conducting wall. However, upon heating the tube to remove the intermediate layer on the fluorescent screen, the intermediate layer on the lateral wall of the tube is also evaporated and/or burned out. As a result, it was found that the metal layer on the lateral wall readily peels ofi which is detrimental to the desired operation of the tube. This peeling, which is probably due to the intermediate layer that has found its way onto the lateral wall, may be avoided by removing said material before applying the metal. However, due to the unusual configurations of modern cathode-ray tubes, some of the parts of the lat- 2,751,515 Patented June 19, 1956 2. eral wall are not easily accessible so that removal of this layer,.which is usually accomplished by brushing, requires special skill on the part of the operator and/or special instruments.

The main object of the invention is to obviate peeling f the metal coating on the lateral wall of a cathoderay tube without employing a method in which the lateral wall has to be brushed.

According tothe invention, a cathode-ray tube comprising a fluorescent screen, which on the side remote from the viewer is coated with a metal layer employing an intermediate layer removable by heating after the metal layer has been applied, is provided with a layer of porous material on at least that part of the lateral wall of the tube to which the temporary intermediate layer may adhere, the metal layer then being provided over the porous material.

The term porous material defining the layer on the lateral Wall is to be understood to mean a material having a structure such that interstices are formed therein which for the most part communicate with one another. The porous layer may be made up of granular or pulverulent material since the grains are naturally separated by interstices communicating with one anodier, provided that they do not interfere with evacuation of the tube. Suitable pulverulent materials are, for example, alundum, sand or zinc-sulphide. Alternatively, it is advantageous to use the same fluorescent material for this porous material as that from which the fluorescent screen in the tube is constituted since this insures the additional advantage that no detrimental eifect occurs if accidentally part of the porous material finds its way onto the fluorescent screen, since the material is the same as the material of the screen and thus is also excited by electrons emitting the same radiation. In such a case, it is not necessary for the grains of the luminescent material of the layer on the lateral wall to be conglomerated as L ghtly as those of the fluorescent screen; hence, a given area of the lateral wall will require less material than a similar area of the fluorescent screen.

It has been found that by providing the porous material on the lateral wall of the tube in accordance with the invention, peeling of the metal on the lateral wall of the cathode-ray tube is completely avoided.

The pulverulent substances constituting the porous layer on the lateral wall may be applied to the glass envelope in any conventional manner, for example, by spraying. Alternatively, the glass envelope may be coated with a binder, e. g., a silicate of sodium or potassium, to hold the powder material. On the other hand, if the fluorescent screen has been applied without a binder, or if the quantity of binding agent on the lateral wall, is not suficient, additional binder may be applied by Washing the lateral Wall with a dilute binder solution. A suitable solution of this kind is a potassium silicate solution. As a further alternative, the powder for the porous layer on the lateral wall may be mixed with or enwrapped in a binding agent.

The invention will now be described with reference to the accompanying drawing in which the sole figure shows partly in cross-section a cathode-ray tube in accordance with the invention.

Referring to the figure, a cathode-ray tube comprises an envelope 2 constituted by a neck portion 3 sealed to a pyramidal portion 4 which, in turn, is sealed to a window 5. The window 5 is coated with a fluorescent material 6. The area at the junction of the pyramidal portion 4 and the window 5, which is adjacent the window, constitutes the lateral Wall 7. This lateral wall 7 is coated on the interior thereof with a porous layer 8 of pulverulent material, e. g., alundum. Both the porous layer 8 and the fluorescent material 6 are provided with a metal layer 9.

While we have thus described our invention with specific examples and embodiments thereof, other modifications will be readily apparent to those skilled in the art without departing from the'spirit and the scope of the invention as defined in the appended claim.

What I claim is: V

A cathode ray tube comprising'an envelope having a cylindrical portion and a conical portion flaring outwardly from said cylindrical portion, a transparent Window sealed to the open end of said conical portion, a layer of luminescent material covering said window portion and extending a substantial distance along the adjoining inner Wall of said conical portion, and a reflective metal layer continuously extending over said luminescent layer on said window and said adjoining wall portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,298,968 Roberts Oct. 13, 1942 2,374,311 Schaefer Apr. 24, 1945 2,582,822 Evans Ian. 15, 1952 2,583,000 Lytle Jan. 22, 1952 2,597,617 Campbell May 20, 1952 2,654,675 Thierferlder Oct. 6, 1953 g ew-2. 

